1. Field of the Invention
The present invention relates to personal watercraft, and more particularly to hydro-jet propulsion systems of personal watercraft.
2. Description of Related Art
Personal watercraft resemble small power boats, having hulls similar in shape but generally smaller than boat hulls. In use, a rider stands, sits or kneels near the stern of the watercraft when riding.
A hydro-jet propulsion system typically powers the watercraft. The propulsion system comprises a motor which drives a pump located in the aft section of the hull. An intake gullet in the bottom of the hull provides a passageway for water entering the pump; the pump, in turn, forces the water through a jet nozzle, thereby propelling the watercraft forward.
Prior gullet designs do not optimize water flow characteristics in the gullet to improve pump efficiency. Typical prior gullet designs have irregular shape intake apertures opening into the gullet and obstructive safety features. Moreover, in some prior gullet designs, the entry edges (i.e., the edges in which water strikes) of the intake aperture are sharp, and, in the plane of the intake aperture, are oblique to the water flowing into the gullet. These designs cause turbulence, air entrainment and other instabilities in the water flow entering the pump.
Turbulent water entering the pump decreases pump performance, as known in the art. Additionally, violent turbulence creates cavitations in the water; cavitation, or bubbles internal to the flow, occurs when the local water pressure decreases below that of the water vapor pressure. Cavitation decreases the volume of liquid flowing through the pump, further reducing its efficiency. Cavities also violently collapse when reaching the pump, imploding and damaging the pump.